Card Suggestions

The more I learn about video cards the more confused I get. Would like suggestions for best gaming card for the following system. AMD 1 gig /512 sdram/PC100/4x AGP. Found out that my Crucial 8500LE 128mb only has memory clock rate of 169 instead of 250. Am trying a Sapphire 9200 256mb that has a lower core clock rate but a higher memory clock rate and have seen some improvement. MY big problem is I only have a 250 watt power supply. I would like to get the best card that has a decent core and clock speed and will run at 250 watts. Have heard that the ATI 8500 or the GeForce Ti4200 would be good but where can I buy these older cards. Hope you guys can help.